Stock Plans (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Summary of Stock Option and RSA Activity

A summary of stock option and RSU activity as of December 31, 2019, and corresponding changes during the year, are as follows:

	Stock Options			Service-Based RSUs			Service and Performance-Based RSUs
(Shares in thousands)	Shares	Weighted-Average Exercise Price		Shares	Weighted- Average Grant Price		Shares	Weighted- Average Grant Price
Outstanding as of December 31, 2018	5,484	$	64.73	2,544	$	80.15	4,022	$	74.22
Granted	408	101.43		1,041	103.93		1,358	90.34
Exercised/vested	(1,626)	51.92		(1,001)	76.07		(1,819)	58.28
Forfeited	(94)	92.19		(172)	89.79		(169)	93.74
Expired	—	—		—	—		—	—
Outstanding as of December 31, 2019	4,172	72.70		2,412	$	91.42	3,392	$	88.25
Options vested and expected to vest as of December 31, 2019	4,171	72.70
Options exercisable as of December 31, 2019	2,357	$	61.15

Weighted-average Remaining Contractual Life and Aggregate Intrinsic Value of the Company's Stock Options Outstanding, Exerciseable, and Vested and Expected to Vest

The weighted-average remaining contractual life and the aggregate intrinsic value (the amount by which the fair value of our stock price exceeds the exercise price of the option) of the stock options outstanding, exercisable, and vested and expected to vest as of December 31, 2019, were as follows:

	Outstanding		Exercisable		Vested and Expected to Vest
Weighted-average remaining contractual life (in years)	5.3		4.0		5.3
Aggregate intrinsic value (millions)	$	216	$	149	$	216

Weighted Average Assumptions Used

The fair value of each option is estimated on the date of grant using a Black-Scholes-Merton option-pricing model. The following weighted-average assumptions were used for options granted in 2019, 2018 and 2017:

	2019			2018			2017
Dividend yield	1.5		%	1.4		%	1.8		%
Expected volatility(a)	24		%	22		%	24		%
Risk-free interest rate	2.6		%	2.7		%	2.3		%
Expected life of stock option (in years)(b)	7.1			7.1			6.9
Weighted-average fair value per option	$	23.38		$	23.17		$	18.18

(a)The expected volatility is based on both weighted historical and implied volatilities of our common stock price.

(b)The expected life of stock options was determined using both historical data and expectations of option exercise behavior.

Therefore, the fair values of these options were estimated at the grant date using a Monte Carlo valuation model with the following assumptions:

	October 31, 2017
Dividend yield	1.58		%
Expected volatility(a)	21.41		%
Risk-free interest rate	2.26		%
Expected life of stock option (in years)	7
Fair value per option	$	19.18

(a)The expected volatility is based on both weighted historical and implied volatilities of our common stock price.

Schedule of Share-based Payment Award, Valuation Assumptions

The fair value of RSUs that do not include the r-TSR modifier, including those that contain only service conditions, is measured using our stock price on the grant date. The fair value of service and performance-based RSUs that include the r-TSR modifier is determined using a Monte Carlo valuation model with the following weighted-average assumptions:

	2019
Expected volatility(a)	20	%
Risk-free interest rate	2.5	%
Remaining performance period (in years)	2.9

(a)The expected volatility is based on historical volatility of our common stock price.